Thermostable and detergent compatible proteases are widely used in food and detergent industries. Common household detergents contain proteolytic enzymes, of which the majority are produced by the members of the genus Bacillus. Although subtilisins have long been the enzymes of choice for detergent formulations, they are not the ideal detergent enzymes because they possess low thermal stability in the presence of detergents and short shelf-life. Enzymes like this have been known for some time. For example, reference is made to the following patents.
U.S. Pat. No. 4,386,160 to Branner-Jorgensen describes a thermally de-stabilized Bacillus serine protease, modified such that the thermal stability is reduced to a level at which the proteolytic activity may be deactivated by a heat treatment.
U.S. Pat. No. 5,346,822 to Vetter et al. describes alkaline Bacillus proteases, their use and a method for producing these proteases. These are in particular Bacillus proteases from Bacillus pumilus DSM 5777.
U.S. Pat. No. 5,427,936 to Moeller et al. describes alkaline Bacillus lipases in combination with proteases, which are suitable for cleaning, washing and bleaching purposes.
An enzyme's resistance to denaturing agents, such as sodium dodecylsulfate (SDS) or urea, is one indication of strong proteolytic activity. Proteases withstanding 1% SDS without undergoing denaturation have commonly been considered as SDS-resistant. Proteases, such as alcalase from B. licheniforms and subtilisin from B. subtilis, have long been used in detergents. Deane et al (1987) reported a SDS-resistant protease but not a SDS-stable protease because the enzyme's proteolytic activity can be restored only after removing SDS. So far, proteinase K (EC 3.4.21.14) from fungal Tritirachium album limber has been considered as the most powerful microbial protease in terms of its stability against SDS. Proteinase K could still retain about 65% its original enzymatic activity in the presence of 6% SDS in its reaction system (Bajorath et al., 1988a).
Enzymes from various sources differ greatly in their catalytic and physical properties. Since it is still unclear so far about the exact function of each amino acid in contributing to the structure of proteins, artificial modification of proteins may not always produce expected results. While site-directed mutagenesis may provide information on the role of some specific amino acid side-chains in protein functionalities, wild-type proteins with some novel properties will give more information on structure-function relations and this in-turn will guide further mutagenic studies in protein science.